Optical amplifier glass

ABSTRACT

An optical amplifier glass comprising a matrix glass containing Bi 2 O 3  and at least one of Al 2 O 3  and Ga 2 O 3 , and Er doped to the matrix glass, wherein from 0.01 to 10% by mass percentage of Er is doped to the matrix glass which has a total content of Al 2 O 3  and Ga 2 O 3  of at least 0.1 mol %, a content of Bi 2 O 3  of at least 20 mol %, a refractive index of at least 1.8 at a wavelength of 1.55 μm, a glass transition temperature of at least 360° C. and an optical basicity of at most 0.49.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical amplifier glass,particularly a broadband optical amplifier glass which is operable in awavelength range of from 1.55 to 1.65 μm.

2. Discussion of Background

For the purpose of application to the optical communication field, therehave been research and development of an optical fiber amplifier usingas an optical amplification medium an optical fiber having a rare earthelement doped to the core, and an Er (erbium)-doped optical fiberamplifier (EDFA), and their application to an optical communicationsystem is being actively pursued. On the other hand, to cope withdiversification of communication services expected in future, awavelength division multiplexing communication system (WDM) has beenproposed to increase the transmission capacity. As the number ofwavelength division multiplexing channels increases, the transmissioncapacity will increase. Application of EDFA to such a wavelengthdivision multiplexing transmission system is also being studied. As EDFAso far proposed, an Er-doped quartz type fiber and an Er-doped fluoridefiber are known.

In the case of a conventional Er-doped quartz type fiber, the wavelengthdependency of the gain is sharp, and the wavelength width wherein anadequate gain is obtainable, is as narrow as from about 10 to 30 nm.Consequently, so far as such conventional EDFA is employed, the numberof wavelength division multiplexing channels is limited to a level offrom 30 to 40 channels.

If EDFA showing a flat gain within a wider wavelength range, isrealized, it is expected to be able to broaden the useful signalwavelength and thereby to substantially improve the transmissioncapacity. Accordingly, development of such EDFA is desired.

In order to solve such problems, an optical amplifier which can be usedin a wide wavelength range has been proposed wherein amplifiers havingdifferent amplification gain characteristics to wavelengths, arearranged in series or in parallel, but there has been a problem suchthat the structure tends to be cumbersome, or in the vicinity of thecenter of the wavelength range, there is a region where no amplificationis possible. Further, JP-A-8-110535 proposes a tellurite type glass as aglass capable of amplification in a broadband range. However, suchtellurite type glass usually has a low glass transition point and isthermally unstable. In order to improve the amplification gain of anoptical amplifier, it is necessary to let a high intensity excited laserbeam enter into the glass, but such glass was likely to be thermallydamaged by the strong laser beam.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-mentionedproblems and to provide an optical amplifier glass having a high glasstransition point and having a wide wavelength width wherein the gain isobtainable.

The present invention provides an optical amplifier glass comprising amatrix glass containing Bi₂O₃ and at least one of Al₂O₃ and Ga₂O₃, andEr doped to the matrix glass, wherein from 0.01 to 10% by masspercentage of Er is doped to the matrix glass which has a total contentof Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, a content of Bi₂O₃ of at least20 mol %, a refractive index of at least 1.8 at a wavelength of 1.55 μm,a glass transition temperature of at least 360° C. and an opticalbasicity of at most 0.49.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With an optical amplifier glass having Er-doped to a matrix glass,optical amplification is carried out by means of stimulated emissiontransition from the ⁴I_(13/2) level to the ⁴I_(15/2) level of Er. Thepresent inventors have found that the wavelength width wherein theoptical amplification gain is obtainable, is dependent on the opticalbasicity which will be described hereinafter, and have thus arrived atpresent invention. The wavelength width within which the opticalamplification gain is obtainable, will hereinafter be referred to as“the gain wavelength width”.

The gain wavelength width has heretofore been considered to be asfollows. Namely, the gain wavelength width is dependent on therefractive index of the matrix glass, i.e. the gain wavelength widthincreases as the refractive index increases. This has been explainedsuch that the electric field which Er receives in the matrix glassincreases as the refractive index increases, and consequently, theenergy level of Er is broadened, whereby the emission spectrum becomesbroad.

However, the present inventors have found that the gain wavelength widthΔλ is not only dependent on the refractive index of the matrix glass butalso strongly dependent on the optical basicity Λ of the matrix glass,which will be described hereinafter, i.e. Δλ becomes large as Λ becomessmall.

With respect to a glass composition represented by mol % of oxidecomponents, the optical basicity Λ is defined as follows. Namely, with aglass containing C_(i) mol % of an oxide of component i,

Λ=1−Σ[z _(i) ·r _(i)(γ_(i)−1)/2γ_(i)]

Σ indicates summing up with respect to subscript i

γ_(i)=1.36(x _(i)−0.26)

z_(i): valency of the cation in the oxide of component i,

r_(i): the ratio of the number of cations in the oxide of component i tothe total number of oxygen in the above “glass composition representedby mol % of oxide components”,

x_(i): the Pauling's electronegativity of an atom bonded to oxygen inthe oxide of component i.

For reference, the Pauling's electronegativities of main atoms are shownbelow.

Li:1.0, Na:0.9, K:0.8, Mg:1.2, Ca:1.0, Sr:1.0, Zn:1.6, Ba:0.9, B:2.0,Al:1.5, Si:1.8, P:2.1, Ge:1.8, Ga:1.6, Te:2.1, Sn:1.8, Sb:1.9, W:1.7,Pb:1.8, Bi:1.9, and Ti:1.5.

For example, with respect to a glass wherein the oxide of the firstcomponent is Bi₂O₃, and the oxide of the second component is SiO₂, andthe composition represented by mol % is 20Bi₂O₃/80SiO₂,

z₁=3, z₂=4

Total number of oxygen=0.2×3+0.8×2=2.2,

r₁=0.2×2/2.2, r₂=0.8×1/2.2,

x₁=1.9, x₂=1.8,

Λ=0.47.

The optical basicity is one which Duffy et al. have proposed as an indexof the basicity of glass in J. Am. Chem. Soc., 93 (1971) 6448, and it isone obtainable by a simple calculation from the glass compositionwithout necessity of carrying out the measurement or complex analysis orcalculation.

Now, the relation between Λ and Δλ will be described based on data.

Glasses A to I having Er doped to a matrix glass having a compositionshown by mol % in lines for from Bi₂O₃ to ZnO in Table 1, were prepared.The amount of Er doped, is shown in the line for Er in Table 1 by mass %based on the matrix glass being 100%. With respect to these glasses, therefractive index n at a wavelength of 1.55 μm, the glass transitionpoint Tg (unit: ° C.) and the gain wavelength width Δλ (unit: nm) weremeasured. Further, the optical basicity Λ was calculated from thecomposition. The measuring methods for n, Tg and Δλ were as follows.

n: measured by an Ellipsometer.

Tg: measured by a differential thermal analysis (DTA).

Δλ: excited by a laser beam with a wavelength of 980 nm, and it wasobtained from the emission spectrum obtained by this excitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relation between the optical basicity Λ ofglass and the wavelength width Δλ (unit: nm) wherein the opticalamplification gain is obtainable.

FIG. 2 is a graph showing the relation between the optical basicity Λ ofan optical amplifier glass of the present invention and the wavelengthwidth Δλ (unit: nm) wherein the optical amplification gain isobtainable.

TABLE 1 A B C D E F G H I Bi₂O₃ — — 40 — — — 20 — — B₂O₃ — — 20 — 20 — —— — SiO₂ — 70 20 — 70 — 50 — 97.9 Al₂O₃ — — — — — — — — 0.1 GeO₂ — — — —— — — — 2 TiO₂ — — — — — — 10 — — TeO₂ 75 — — 75 — 75 — 75 — Na₂O 5 2020 20 10 15 10 7 — CaO — 10 — — — — — — — BaO — — — — — — 10 — — ZnO 20— — 5 — 10 — 18 — Er 0.5 0.5 0.5 2.5 1.0 1.0 0.5 0.5 0.05 n 2 1.5 2 1.91.5 1.92 1.8 1.97 1.49 Tg 299 550 370 270 490 285 470 292 1010 Λ 0.4380.587 0.505 0.490 0.495 0.455 0.547 0.445 0.478 Δλ 69 18 30 35 32 48 2259 3838

FIG. 1 is a graph wherein the relation between Λ and Δλ in Table 1, wasplotted.

As is evident from FIG. 1, Δλ increases as Λ becomes small. The reasonis not clearly understood, but it is considered that in a matrix glasshaving small Λ, the polarizability of O (oxygen) ions surrounding Erions tends to decrease, whereby the electrical shielding effect of Erions tends to be large, and consequently, the proportion of the electricdipole transition to the magnetic dipole transition of Er tends to belarge.

Further, as is evident from Table 1, even with glasses havingsubstantially the same refractive index n, Δλ is not necessarily thesame. For example, n of each of glass A and glass C is 2, Δλ of glass Ais 69 nm, and Δλ of glass C is 30 nm, and thus, the difference in Δλ ofthe two is substantial. Such a difference can not be expected by theconventional concept such that Δλ is dependent largely on n, and can beexpected for the first time by the discovery relating to Λ and Δλ by thepresent inventors.

The optical amplifier glass of the present invention is used usually inthe form of a fiber.

In the optical amplifier glass of the present invention, from 0.01 to10% by mass percentage of Er is doped in the matrix glass. Here, thematrix glass is regarded as 100%. The matrix glass in the opticalamplifier glass of the present invention will be referred to hereinaftersimply as the matrix glass of the present invention.

If the amount of Er is less than 0.01%, the desired opticalamplification can not be obtained. Preferably, it is at least 0.1%, morepreferably at least 0.3%. If it exceeds 10%, optical quenching byconcentration tends to occur, whereby the optical amplification tends todecrease. It is preferably at most 5%, more preferably at most 1%. Whenthe optical amplifier glass of the present invention is used in the formof a fiber, the amount of Er is preferably adjusted depending upon thelength of the fiber. Namely, it is preferred that when the fiber islong, the amount is adjusted to be small, and when the fiber is short,the amount is adjusted to be large.

The refractive index at a wavelength of 1.55 μm of the matrix glass ofthe present invention is at least 1.8. If it is less than 1.8, theelectric dipole transition of Er tends to hardly take place, whereby Δλtends to be too small. It is preferably at least 1.9, more preferably atleast 2.0.

The glass transition point of the matrix glass of the present inventionis at least 360° C. If it is less than 360° C., when the temperature ofglass becomes locally high by the use of a laser beam of high intensityas an excitation light, the glass tends to be thermally damaged, and thedesired optical amplification tends to hardly be obtained. It ispreferably at least 380° C., more preferably at least 400° C.

The optical basicity of the matrix glass of the present invention is atmost 0.49. If it exceeds 0.49, Δλ tends to be too small. It ispreferably at most 0.485, more preferably at most 0.48.

To reduce the optical basicity, it is preferred to introduce into theglass atoms having large values of the above-mentioned z_(i) (valency ofthe cation) and/or the above-mentioned x_(i) (the Pauling'selectronegativity of atoms). As such atoms, Bi, Si, Al or Ga may, forexample, be mentioned. Accordingly, it is preferred that the matrixglass of the present invention is a Bi₂O₃/SiO₂/M₂O₃ type glass. Here,M₂O₃ is Al₂O₃ and/or Ga₂O₃.

Now, the composition of the matrix glass of the present invention willbe described, wherein mol % will be represented simply as %.

Bi₂O₃ is an essential component. If it is less than 20%, the electricdipole transition of Er tends to hardly occur, whereby Δλ tends to betoo small. It is preferably at least 25%, more preferably at least 30%.Further, its content is preferably at most 80%. If it exceeds 80%,vitrification tends to be difficult, or devitrification tends to takeplace during processing into a fiber, or the glass transition pointtends to be too low. Preferably, it is at most 70%, more preferably atmost 65%. Here, devitrification is meant for distinct precipitation ofcrystals, which causes breakage of the fiber during the fiber processingor the breakage of the fiber during use as an optical amplifier glassfiber.

At least one of Al₂O₃ and Ga₂O₃ must be contained. If the total contentthereof is less than 0.1%, crystallization of glass is likely to takeplace. It is preferably at least 1%. Further, the total content ispreferably at most 30%. If it exceeds 30%, vitrification tends to bedifficult, or the glass transition point tends to be too low. It is morepreferably at most 25%.

The content of Al₂O₃ is preferably at most 10%. If it exceeds 10%, theoptical amplification is likely to deteriorate. It is more preferably atmost 8%, particularly preferably at most 6%. When Al₂O₃ is contained,the content is preferably at least 0.1%, more preferably at least 1%.

The content of Ga₂O₃ is preferably at most 30%. If it exceeds 30%, theoptical amplification is likely to deteriorate, or the glass transitionpoint is likely to be too low. It is more preferably at most 20%. WhenGa₂O₃ is contained, the content is preferably at least 0.1%, morepreferably at least 1%.

B₂O₃ is not an essential component, but it is a network former and ispreferably contained in a range of up to 75% in order to facilitateformation of glass by suppressing precipitation of crystals during thepreparation of glass. It is more preferably at most 50%, particularlypreferably at most 30%. When B₂O₃ is contained, the content ispreferably at least 1%.

Further, in some cases, it is preferred that the B₂O₃ content is lessthan 15%. For example, such is preferred when the total content of Al₂O₃and Ga₂O₃ exceeds 1%.

SiO₂ is not an essential component, but it is a network former and ispreferably contained in a range of up to 79.9% in order to facilitateformation of glass by suppressing precipitation of crystals during thepreparation of glass. It is more preferably at most 50%, particularlypreferably at most 40%. When SiO₂ is contained, the content ispreferably at least 1%.

Further, the total content of Bi₂O₃ and SiO₂ is preferably at least 50%.

In order to facilitate formation of glass by suppressing precipitationof crystals during the preparation of glass, it is preferred toincorporate at least one of B₂O₃ and SiO₂. The total content thereof ispreferably within a range of from 5 to 60%. If it is less than 5%,vitrification is likely to be difficult, or the optical amplificationtends to be inadequate, or devitrification is likely to occur during thefiber processing. It is more preferably at least 10%, particularlypreferably at least 15%. If it exceeds 60%, the optical amplification islikely to be inadequate. It is more preferably at most 55%, particularlypreferably at most 50%.

GeO₂ is not essential, but it facilitates formation of glass and has aneffect to increase the refractive index. Thus, it may be doped up to30%. If it exceeds 30%, the glass tends to crystallize. It is preferablyat most 10%, more preferably at most 5%. When GeO₂ is contained, thecontent is preferably at least 0.1%, more preferably at least 1%.

Each of Li₂O, TiO₂, ZrO₂ and SnO₂ is not essential, but each of them maybe doped within a range of up to 50% in order to suppressdevitrification during fiber processing. Each content is preferably atmost 10%.

WO₃ is not essential but may be doped up to 30% in order to increase Δλ.If the content exceeds 30%, the optical amplification is likely todeteriorate. It is more preferably at most 20%, particularly preferablyat most 10%.

TeO₂ is not essential but may be doped up to 30% in order to increaseΔλ. If the content exceeds 30%, the optical amplification is likely todeteriorate. It is more preferably at most 20%, particularly preferablyat most 17%.

The total content of WO₃ and TeO₂ is preferably at most 27%. If thetotal content exceeds 27%, crystals are likely to precipitate, wherebyvitrification or fiber processing tends to be difficult. It is morepreferably at most 20%, particularly preferably at most 15%.

CeO₂ is not essential, but it has an effect to suppress reduction ofBi₂O₃ in the glass composition during melting of glass to precipitatemetal bismuth thereby to lower the transparency of glass and may bedoped up to 10%. If it exceeds 10%, vitrification tends to be difficult.It is more preferably at most 1%, particularly preferably at most 0.5%.

Further, if CeO₂ is contained, it may happen that yellow or orangecoloring tends to increase, whereby the transmittance of glass tends todecrease, and the background loss at an excitation light wavelength(such as 980 nm) or a signal light wavelength tends to increase. Fromthis viewpoint, the content of CeO₂ is preferably less than 0.15%,particularly preferably substantially zero.

It is preferred that the matrix glass of the present invention consistsessentially of the above described components, but components other thanthe above described components (“other components”) may be containedwithin a range not to impair the purpose of the present invention. Forexample, to facilitate vitrification or to suppress devitrificationduring fiber processing, BeO, MgO, CaO, SrO, BaO, Na₂O, K₂O, Cs₂O,La₂O₃, ZnO, CdO, In₂O₃ or PbO may, for example, be contained. The totalcontent of such other components is preferably not more than 10%.

As a preferred composition of the matrix glass of the present invention,the following may be mentioned, as represented by mol % based on thefollowing oxides:

Oxides Mol % Bi₂O₃ 20 to 80, B₂O₃  0 to 75, SiO₂  0 to 79.9, Al₂O₃  0 to10, Ga₂O₃  0 to 30, GeO₂  0 to 30, Li₂O  0 to 50, TiO₂  0 to 50, ZrO₂  0to 50, SnO₂  0 to 50, WO₃  0 to 30, TeO₂  0 to 30, and CeO₂  0 to 10,

wherein at least one of B₂O₃ and SiO₂ is contained, and the totalcontent of Al₂O₃ and Ga₂O₃ is at least 0.1 mol %.

The method for preparing the optical amplifier glass of the presentinvention is not particularly limited, and it can be prepared by mixingthe prescribed starting materials, putting the mixture into a platinumcrucible, an alumina crucible, a quartz crucible or an iridium crucible,melting it in air at a temperature of from 800 to 1,300° C., and castingthe obtained melt in a prescribed mold. Otherwise, it may be prepared bya method other than the melting method, such as a sol gel method or agas phase vapor deposition method.

From the glass thus prepared, a preform may be prepared and formed intoa fiber, or such a glass may be formed into a fiber by a double cruciblemethod, to obtain an optical amplifier fiber.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

EXAMPLES

Glasses 1 to 10 were prepared which had Er doped to the matrix glasseshaving the compositions shown by mol % in lines from Bi₂O₃ to CeO₂ inTable 2. The amount of Er doped is represented by mass %, based on thematrix glass being 100%. With respect to each of these glasses, therefractive index n at a wavelength of 1.55 μm, the glass transitionpoint Tg (unit: ° C.) and the gain wavelength width Δλ (unit: nm) weremeasured by the above-mentioned methods. Further, from the composition,the optical basicity Λ was calculated. Glasses 1 to 9 represent WorkingExamples of the present invention. Glass 10 is an Er-doped quartz typeglass which is the same as glass 1 in Table 1 and represents aComparative Example.

FIG. 2 is a graph wherein the relation between Λ and Δλ in Table 2 wasplotted. As is evident from this Figure, Δλ increases as Λ becomessmall. Here, Δλ is preferably at least 40 nm.

TABLE 2 1 2 3 4 5 6 7 8 9 10 Bi₂O₃ 43 43 43 45 40 43 43 43 62.8 — B₂O₃ —— — 5 1 27 28 28 30 — SiO₂ 29 36 22 20 20 20 21 14 4 97.9 Al₂O₃ 3 3 3 22 1 — 1 — 0.1 Ga₂O₃ 18 18 18 8 19 — 1 — 3 2 GeO₂ — — — — — 2 — — — —TiO₂ — — — — 6 — — — — — SnO₂ — — — 6 — — — — — — WO₃ — — — 2 2 7 — — —— TeO₂ 7 — 14 12 10 — 7 14 — — CeO₂ — — — — — — — — 0.2 — Er 0.5 0.5 0.52.5 1.0 1.0 0.5 0.5 0.5 0.05 n 2.02 2.01 2.01 2.10 2.05 2.01 2.01 2.022.21 1.49 Tg 450 475 420 440 445 420 415 410 370 1010 Λ 0.478 0.4820.473 0.462 0.482 0.452 0.443 0.440 0.444 0.478 Δλ 42 40 45 50 50 58 6974 68 38

By employing the optical amplifier glass of the present invention,optical amplification within a broader band will be possible, andtransmission of information of a large capacity by a wavelength divisionmultiplexing transmission system will be possible. Further, the thermaldamage scarcely occurs even if a high intensity laser beam is used asthe excitation light.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The entire disclosure of Japanese Patent Application No. 2000-17448filed on Jan. 26, 2000 including specification, claims, drawings andsummary are doped herein by reference in its entirety.

What is claimed is:
 1. An optical amplifier glass comprising a matrixglass comprising the following oxides: Oxides Mol % Bi₂O₃ 20 to 80, B₂O₃ 0 to 75, SiO₂  0 to 79.9, Al₂O₃  0 to 10, Ga₂O₃  0 to 30, GeO₂  0 to30, Li₂O  0 to 50, TiO₂  0 to 50, ZrO₂  0 to 50, SnO₂  0 to 50, WO₃  0to 30, TeO₂  0 to 30, and CeO₂  0 to 10

wherein at least one of B₂O₃ and SiO₂ is contained, and Er doped to saidmatrix glass, wherein from 0.01 to 10% by mass percentage of Er is dopedto said matrix glass which has a total content of Al₂O₃ and Ga₂O₃ of atleast 0.1 mol %, a content of Bi₂O₃ of at least 20 mol %, a refractiveindex of at least 1.8 at a wavelength of 1.55 μm, a glass transitiontemperature of at least 360° C., an optical basicity of at most 0.49. 2.The optical amplifier glass as claimed in claim 1, wherein said B₂O₃ isin a content of at most 30 mol %.
 3. The optical amplifier glass asclaimed in claim 1, wherein said SiO₂ is in a content of from 1 to 50mol %.
 4. The optical amplifier glass as claimed in claim 1, wherein 0.3to 5.0% by mass percentage of Er is doped to said matrix glass.
 5. Theoptical amplifier glass as claimed in claim 1, wherein said refractiveindex is at least 2.0.
 6. The optical amplifier glass as claimed inclaim 1, wherein said Al₂O₃ is in a content of 0.1 to 10 mol %.
 7. Theoptical amplifier glass as claimed in claim 1, wherein said Ga₂O₃ is ina content of 1 to 19 mol %.
 8. The optical amplifier glass as claimed inclaim 1, wherein said GeO₂ is in a content of 0.1 to 30 mol %.
 9. Theoptical amplifier glass as claimed in claim 1, wherein said CeO₂ is in acontent of at most 0.15 mol %.
 10. The optical amplifier glass asclaimed in claim 1, wherein said matrix glass contains substantially noCeO₂.
 11. The optical amplifier glass as claimed in claim 1, whereinsaid B₂O₃ is in a content of less than 15 mol %.
 12. An opticalamplifier glass comprising a matrix glass comprising the followingoxides: Oxides Mol % Bi₂O₃ 20 to 80, B₂O₃  0 to 75, SiO₂  0 to 79.9,Al₂O₃  0 to 10, Ga₂O₃  0 to 30, GeO₂  0 to 30, Li₂O  0 to 50, TiO₂  0 to50, ZrO₂  0 to 50, SnO₂  0 to 50, WO₃  0 to 30, TeO₂  0 to 30, and CeO₂ 0 to 10; and

at least one of B₂O₃ and SiO₂ is contained, at least one of Al₂O₃ andGa₂O₃ is contained, Er doped to said matrix glass, and no K₂O iscontained, wherein from 0.01 to 10% by mass percentage of Er is doped tosaid matrix glass which has a total content of Al₂O₃ and Ga₂O₃ of atleast 0.1 mol %, a refractive index of at least 1.8 at a wavelength of1.55 μm, a glass transition temperature of at least 360° C., an opticalbasicity of at most 0.49.
 13. The optical amplifier glass as claimed inclaim 12, wherein said B₂O₃ is in a content of at most 30 mol %.
 14. Theoptical amplifier glass as claimed in claim 12, wherein said SiO₂ is ina content of from 1.0 to 50 mol %.
 15. An optical amplifier glasscomprising a matrix glass comprising the following oxides: Oxides Mol %Bi₂O₃ 20 to 80, B₂O₃  0 to 75, SiO₂  0 to 79.9, Al₂O₃  0 to 10, Ga₂O₃  0to 30, GeO₂  0 to 30, Li₂O  0 to 50, TiO₂  0 to 50, ZrO₂  0 to 50, SnO₂ 0 to 50, WO₃  0 to 30, TeO₂  0 to 30, and CeO₂  0 to 10; and

at least one of B₂O₃ and SiO₂ is contained, at least one of Al₂O₃ andGa₂O₃, and Er doped to said matrix glass, wherein from 0.01 to 10% bymass percentage of Er is doped to the matrix glass which has a totalcontent of Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, a refractive index ofat least 1.8 at a wavelength of 1.55 μm, a glass transition temperatureof at least 360° C., an optical basicity of at most 0.485.
 16. Theoptical amplifier glass as claimed in claim 15, wherein said B₂O₃ is ina content of at most 30 mol %.
 17. The optical amplifier glass asclaimed in claim 15, wherein said SiO₂ is in a content of from 1 to 50mol %.
 18. An optical amplifier glass comprising a matrix glasscomprising Bi₂O₃, at least one of Al₂O₃ and Ga₂O₃, Er doped to saidmatrix glass, and no K₂O, wherein from 0.01 to 10% by mass percentage ofEr is doped to said matrix glass which has a total content of Al₂O₃ andGa₂O₃ of at least 0.1 mol %, a content of Bi₂O₃ of at least 20 mol %, arefractive index of at least 1.8 at a wavelength of 1.55 μm, a glasstransition temperature of at least 360° C., an optical basicity of atmost 0.49, and said Al₂O₃ is in a content of 0.1 to 10 mol %.
 19. Anoptical amplifier glass comprising a matrix glass comprising Bi₂O₃, atleast one of Al₂O₃ and Ga₂O₃, and Er doped to said matrix glass, whereinfrom 0.01 to 10% by mass percentage of Er is doped to the matrix glasswhich has a total content of Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, acontent of Bi₂O₃ of at least 20 mol %, a refractive index of at least1.8 at a wavelength of 1.55 μm, a glass transition temperature of atleast 360° C., an optical basicity of at most 0.485, and said Al₂O₃ isin a content of 0.1 to 10 mol %.
 20. An optical amplifier glasscomprising a matrix glass comprising Bi₂O₃, at least one of Al₂O₃ andGa₂O₃, Er doped to said matrix glass, and no K₂O, wherein from 0.01 to10% by mass percentage of Er is doped to said matrix glass which has atotal content of Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, a content ofBi₂O₃ of at least 20 mol %, a refractive index of at least 1.8 at awavelength of 1.55 μm, a glass transition temperature of at least 360°C., an optical basicity of at most 0.49, and said Ga₂O₃ is in a contentof 1 to 19 mol %.
 21. An optical amplifier glass comprising a matrixglass comprising Bi₂O₃, at least one of Al₂O₃ and Ga₂O₃, and Er doped tosaid matrix glass, wherein from 0.01 to 10% by mass percentage of Er isdoped to the matrix glass which has a total content of Al₂O₃ and Ga₂O₃of at least 0.1 mol %, a content of Bi₂O₃ of at least 20 mol %, arefractive index of at least 1.8 at a wavelength of 1.55 μm, a glasstransition temperature of at least 360° C., an optical basicity of atmost 0.485, and said Ga₂O₃ is in a content of 1 to 19 mol %.
 22. Anoptical amplifier glass comprising a matrix glass comprising Bi₂O₃, atleast one of Al₂O₃ and Ga₂O₃, Er doped to said matrix glass, no K₂O, andGeO₂ in a content of 0.1 to 30 mol %, wherein from 0.01 to 10% by masspercentage of Er is doped to said matrix glass which has a total contentof Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, a content of Bi₂O₃ of at least20 mol %, a refractive index of at least 1.8 at a wavelength of 1.55 μm,a glass transition temperature of at least 360° C., and an opticalbasicity of at most 0.49.
 23. An optical amplifier glass comprising amatrix glass comprising Bi₂O₃, at least one of Al₂O₃ and Ga₂O₃, Er dopedto said matrix glass, and GeO₂ in a content of 0.1 to 30 mol %, whereinfrom 0.01 to 10% by mass percentage of Er is doped to the matrix glasswhich has a total content of Al₂O₃ and Ga₂O₃ of at least 0.1 mol %, acontent of Bi₂O₃ of at least 20 mol %, a refractive index of at least1.8 at a wavelength of 1.55 μm, a glass transition temperature of atleast 360° C., an optical basicity of at most 0.485.